Apparatus for stormwater retention and release, and method of use thereof

ABSTRACT

Apparatus and a method are aimed at reducing flood risk from stormwater draining from a property ( 1 ). The apparatus is adapted in use to retain stormwater at the property ( 1 ) releasing it from the property and comprises a container ( 6 ) which in use is located underneath or proximal to a building ( 2 ) of the property ( 1 ), and a control chamber ( 3 ) with which the container ( 6 ) is in fluid communication. The apparatus is operatively connected in use by at least one conduit ( 4 ) to drainage means ( 5 ) sourced externally from the building to receive stormwater into the container ( 6 ) by way of the control chamber ( 3 ), and is further operatively connected in use to at least a second conduit ( 7 ) to which stormwater exits from the container ( 6 ) by way of the control chamber ( 3 ). A level of stormwater in the control chamber ( 3 ) determines the inflow and outflow of stormwater into and from the container ( 6 ). Debris is prevented at the control chamber from entering into the container and passing to the second conduit ( 7 ). Stormwater may be pumped from the container for watering a garden or other uses. The property ( 1 ) may comprise a series of buildings ( 2 ), each with its own stormwater retention.

This invention relates to apparatus for stormwater retention andrelease, and a method of use thereof. The invention relates morespecifically to, but is not limited to, apparatus for stormwaterretention and release from a property development.

The term stormwater encompasses water deposited by the weather, andincludes snow, hail, rain and ice.

Property developments, especially residential developments, morefrequently require that stormwater draining from the property isretained prior to its controlled release in order to reduce flood risksdownstream of the site, or to control flows of existing points ofoutfall with limited spare capacity. Frequently, rates of stormwaterdischarge from property developments are carefully controlled andrestricted, certain controlled rates being set to particularly lowlevels resulting in large balancing means being necessary to retain thestormwater prior to its controlled release.

The two most frequently used solutions to retain stormwater compriseproviding balancing means in the form of a pond or a relatively largetank located in an open space area proximal to the development. If atank is provided, it may be located under a highway as part of a boxculvert. Stormwater collects in the tank or pond and is retained thereinprior to release through suitably dimensioned outlets into a localdrainage network, usually a sewer.

Ponds are less favoured by developers as they require regularmaintenance, and controls connecting the pond to a local drainagenetwork are susceptible to blockage by debris fang into or otherwisegaining access to the pond. Tanks, however, are expensive and alsorequire regular maintenance. Often, developable land must be sacrificedin order to accommodate the pond or tank.

Furthermore, ponds and tanks of the prior art type are laborious toinstall. Large sewers, usually in the form of relatively large diameterpipework, or box culverts, must be installed underground which requiresa significant amount of effort.

Whilst not concerned with control of stormwater control at propertydevelopments to reduce flood risks there is disclosure in EP 08253304 A2of apparatus for separating floating and non-floating particulate fromdrain water in sudden storms and in steady prolonged rainfall. A tank isconnected to inlet and outlet conduits to provide a level of drain waterbetween the conduits and includes particulate containment chambers inwhich particulate is collected from the water passing through the bankfrom the inlet to the outlet conduit. In one embodiment a detentionbasin is provided in combination with the tank into which excessivedrain water resulting from higher than usual water flow rates isdiverted from the tank. Drain water from the detention basin returns tothe tank by a one-way valve for exit from the outlet conduit once thesudden influx of water has passed. The diverted water enters thedetention basin at a much higher level than the entry to the outletconduit, which is in the lower region of the tank. The one-way valve isat the level of the entry to the outlet conduit so that the water isencouraged to leave the detention basin as soon as the sudden influx ofwater passes. This disclosure is essentially concerned with removal ofparticulate in a sewer system rather than drain water storage to reduceflood risks.

DE 29611700 U1 discloses the collection of rainwater underneath abuilding but this is to provide a reservoir of the water for pumping toshower/washing facilities in the building and is not intended to reduceflood risk at a property. Drainage pipes simply feed and drain waterdirectly into and from the foundations of the building where the wateris collected.

There is a need in the art for apparatus which can effect stormwaterretention and where necessary, controlled release of stormwater from aproperty development, which overcomes problems discussed above.

According to a first aspect of the invention there is providedstormwater retention apparatus adapted in use to retain stormwater priorto release of the stormwater from a property comprising:

a closed container which in use is located underneath or proximal to abuilding of the property, being operatively connected in use by at leastone inlet conduit to drainage means sourced externally from the buildingto receive stormwater into the container, and being further operativelyconnected in use to at least one outlet conduit by which stormwater isled away from the container and

a control chamber with which the container is in fluid communication andthrough which stormwater enters, to be stored in, and leaves thecontainer when the stormwater reaches a determining level (W) in thecontrol chamber spaced above the base of the container,

characterised in that the inlet and outlet conduits are connected to thecontrol chamber and thereby to the container, and that the outletconduit comprises an end portion which passes out of the control chamberand includes an entry spaced above the determining level (W) by whichstormwater can pass from the control chamber into the end portion toexit from the control chamber, and which by being spaced above thedetermining level (W) allows stormwater to collect in the container andcontrol chamber above the determining level (W).

The property may be one of a series of properties on a propertydevelopment. Preferably each property in such a development hasstormwater retention apparatus according to the first aspect of theinvention, the stormwater exiting from the container of each apparatusinto a local sewer.

Preferably the container is subterranean, located under part of theproperty. Where the property is a house having a garage, the containeris conveniently located under the garage, for example.

Advantageously, no pond or tank is required, freeing all availabledevelopable land. As the container of the or each stormwater retentionapparatus and its conduits are of a considerably smaller scale thanprior art ponds and tanks, considerably less effort is required toinstall apparatus according to the first aspect of the invention.

Furthermore, the apparatus is less susceptible to blockage as verylittle debris can gain access to the container as it may be sealed offfrom the environment. Small amounts of debris, such as leaves, may enterthe container via the drainage means fitted to the property, but ingeneral are not sufficient to block the entry to the outlet conduit.

Preferably the container is incorporated in the foundations of theproperty during construction of the property. Preferably the containeris made at least in part of bricks and mortar, and may be lined withcement. A waterproof lining may be added to the inside surfaces of thecontainer to prevent leaks occurring.

Drainage means fitted externally to the property preferably comprisesguttering and drainpipes which collect stormwater falling on theproperty, channelling the stormwater to the base of the property andinto the container. The drainage means may, however, be any suitabledrainage means which is operatively connectable to the container.

The inlet and outlet conduits may be pipes of relatively narrowdiameter, for example 75 mm or 100 mm.

Where the discharge from the property is rate limited, the apparatus mayinclude suitable exit rate limiting means. The exit rate limiting meansmay include a Hydrobrake (Registered Trade Mark). The outlet conduit mayinclude an orifice which is suitably dimensioned so as to restrict theflow of stormwater through the orifice to a predetermined level.

Where no discharge rate applies, no exit rate limiting means isrequired. In either case, the need for a large tank or pond is obviatedby the provision of apparatus according to the first aspect of theinvention.

Stormwater entering the container must first pass through the controlchamber. The control chamber may be located above or below ground level,or may be partially below ground level. The chamber may be below groundlevel at a level relating to the invert of the container. The controlchamber may be attached to the side of the property underneath which thecontainer is located.

The control chamber may be operatively connected to the container by ahole or holes located in a wall separating the container and the controlchamber. The control chamber may be raised above the level of thecontainer to create a split-level stormwater retention apparatus, thestormwater entering the control chamber and passing under gravity intothe container via a hole or holes in the separating wall proximal to thebase of the control chamber.

The outlet conduit may comprise at least one outlet pipe, an end portionof which sealingly passes through a hole in a wall of the controlchamber. The end portion preferably includes a bend, preferably at 90°,so that one open end of the outlet pipe is directed upwards, away fromthe base of the control chamber. In the wall of the pipe on theunderside of the bend, opposite to the base of the control chamber, asuitably dimensioned orifice may be provided at a selected level throughwhich a restricted flow of stormwater can pass out of the controlchamber when the stormwater in the control chamber reaches that level.

As the stormwater level rises in the control chamber, the orifice doesnot become obstructed as debris floating in the stormwater also rises.When the stormwater level rises above the height of the orifice, a smalljet is created from the orifice into the pipe, operating under a head ofstormwater and ensuring that the orifice remains free of debris.

The control chamber may, at its base, be fitted with a silt trap inwhich biodegradable debris such as leaves can collect without blockingthe passage of stormwater into or out of the container. A weir or weirsto the inlet conduit or conduits may also prevent any solid passing tothe container or obstructing the orifice.

In the above-described form of the outlet conduit, the upwardly-directedopen end of the outlet pipe acts as an overflow outlet. If thestormwater level in- the container rises above the level of the open endof the outlet pipe, stormwater enters the pipe via the open end of thepipe (in addition to exiting via the orifice situated on the undersideof the bend portion of the outlet pipe). The open end is preferablycapped with a device which prevents debris entering the outlet pipe inthe event of an overflow. The device may be a bird-cage cap to preventdebris accessing the outlet pipe and rodent access into the containerfrom a downstream sewer network.

In order to prevent condensation and damp causing damage to thefoundations and underside of the property above the container, airbricks may be included in the upper regions of the foundations to allowventing of water vapour. The air bricks may be provided with insectscreens to prevent debris entering the container. The air bricks mayalso provide a second means of overflow.

Polythene membranes or other waterproof coating such as “SYNTHAPRUFE”(Registered Trade Mark) could be used to line the walls or underside ofthe floor of the property to protect the property from structural damagecaused by damp. In this way, the property is protected from thedeteriorating effects of damp as condensation is isolated by themembranes. In any event, it is designed so that stormwater wouldnormally only be retained in the container for a relatively short periodafter entering the container.

A pump may be provided which pumps stormwater out of the container torecycle the stormwater for other uses, such as watering a garden,flushing toilets or washing a car.

According to a second aspect of the invention there is provided aproperty comprising a building characterised in that it includesstormwater retention apparatus according to the first aspect of theinvention

According to a third aspect of the invention, there is provided a methodof retaining and controlling discharge of stormwater collected bydrainage means fitted to a building, the method comprising the steps ofcollection of stormwater by said drainage means, retention of thestormwater by stormwater retention apparatus according to the firstaspect of the invention, and controlled release of the retainedstormwater by the stormwater retention apparatus into local drainagefacilities.

There now follows, by way of example only, a detailed description of anembodiment of the invention with reference to the accompanying drawingsof which:

FIG. 1 shows a plan view of two adjacent properties of a propertydevelopment which include apparatus according to the first aspect of theinvention;

FIG. 2 shows a plan view of apparatus according to the first aspect ofthe invention provided underneath adjoining garages of the twoproperties of FIG. 1;

FIG. 3 is an enlarged sectional view along the line 3—3 of a controlchamber of the apparatus shown in FIG. 2;

FIG. 4 is a sectional view along the line 4—4 of a container of theapparatus shown in FIGS. 2;

FIG. 5 is a fragmentary sectional view of the floor of one of thegarages looking in the direction of the arrows 5—5 in FIG. 2;

FIG. 6 is a sectional view of an alternative embodiment of the controlchamber; and

FIG. 7 is a plan view of the control chamber of FIG. 6.

FIG. 1 shows part of a property development 1, the part comprising twoadjacent houses 2 with adjoining garages built as a divided doublegarage 2 a. Adjacent the double garage 2 a is a control chamber 3. Thecontrol chamber 3 is located underground, adjacent the foundations (seeFIG. 3) of the double garage 2 a. Conduits in the form of inlet pipes 4feed stormwater into the control chamber 3 from the drainage means 5 ofthe adjacent houses 2 and the garage itself 2 a. The drainage means 5generally comprises drainpipes and guttering which collect stormwaterfalling on the property. A container 6 (see FIG. 2) located under thedouble garage is operatively connected to the control chamber 3. Wallsof the container 6 are defined by the footings of the walls of thedouble garage 2 a, as can be seen in FIG. 4.

The control chamber 3 may have a concrete base, brick walls and beclosed at the top by an access cover. Alternatively, it may be apre-formed unit, for example of a suitable plastics material such asupvc.

An outlet conduit 7 allows stormwater to exit from the control chamber3. The conduit 7 merges with other conduits 7′ carrying stormwater fromfurther properties (not shown), feeding the stormwater into a sewer 8running beneath a nearby road 9.

The double garage 2 a, the control chamber 3 and the conduits 4,7 can beseen in more detail in FIG. 2.

The garage 2 a, as shown in FIG. 2, is rectangular in plan and dividedalong its length into halves by a partition wall 10. The control chamber3 is also rectangular in plan, although any suitable dimensions whichallow the control chamber 3 to be located proximal to the foundations ofthe garage 2 a would suffice. The partition wall divides the containerinto two equally-sized sub-chambers 26,27.

Inlet conduits 4 in the form of pipes feed stormwater into the controlchamber 3. The outlet conduit 7 also in the form of a pipe provides anoutlet for stormwater from the control chamber 3. The inlet and outletconduits 4, 7 are typically 75 mm or 100 mm diameter. The outlet conduit7 includes an end portion 11 which sealingly passes through a wall 12 ofthe control chamber 3 and has an upwardly-directed open end 13.

Holes 14 in a wall 15 of the container, separating the control chamber 3and the container 6, allow water to pass from the control chamber 3 intothe two sub-chambers 26, 27 of the container 6, and vice-versa.

Air bricks 16 at the base of opposite side walls 17,18 of the garage 2 aallow venting of water vapour in the container 6. The air bricks 16 alsoprovide another means of overflow.

In FIG. 3 the control chamber 3 of FIGS. 1 and 2 can be seen in detail.Inlet pipes 4, delivering water from the drainage means of the property,enter the control chamber 3 at a fixed height above the base 3 a of thecontrol chamber 3. The soffit of the inlet pipes 4 is typicallyapproximately 25 mm above the maximum possible level of stormwater inthe control chamber 3, as indicated by the line M, to prevent the inletpipes 4 becoming surcharged. If water level is above the stormwaterdelivery height of the inlet pipes 4, the pipes would become surcharged,impeding the flow of stormwater into the control chamber 3.

The end portion 11 of the outlet conduit 7 has a bend 19, from which theend portion extends upwards away from the base 3 a of the controlchamber 3 to the open end 13, The open end 13 is fitted with a bird cagecap 20, which prevents debris entering the outlet pipe 7 and causing ablockage. This also prevents rodents entering the system from thedownstream sewer network 8.

An orifice 21 is formed in the underside of the bend 19 of the endportion 11. As the water level in the control chamber rises, stormwaterenters the outlet conduit 7 through the orifice 21, as indicated by thearrow X, thereby exiting in a restricted flow from the control chamber 3into the nearby sewer 8.

The position of the orifice 21 in the bottom of the bend of the endportion 11 of the outlet conduit prevents debris collecting in theorifice 21 after the water level has fallen. Debris in the controlchamber 3 may rise with the water level to, and above, the level of theorifice 21 but after the water level has dropped, gravity preventsdebris accumulation in the orifice 21. Furthermore, when stormwatergathers in the control chamber to a level above the level indicated bythe line W in FIG. 3, the orifice 21 is submerged in the stormwater, anda restricted flow of stormwater escapes into the outlet conduit 7,through the orifice 21, generating a flume in the outlet conduit fromthe orifice 21 which ensures that the orifice 21 cannot become blocked.

The holes 14 in the wall 15 between the control chamber 3 and thecontainer 6 allow stormwater to enter the container 6 when the waterlevel in the control chamber rises above the water level W.

The container 6 has a closed roof formed by the underside of a block andbeam floor 23 of the double garage 2 a. A water proofing membrane, forexample of SYNTHAPRUFE 22 (Registered Trade Mark), is applied to theunderside of the roof of the container. This waterproofing membraneprotects the garage 2 a from damp effecting steel work in the beams ofthe floor 23.

In addition, the air bricks 16 allow the escape of excess stormwaterfrom the container 6, for example in the event of extreme flooding orcollection of stormwater in the container 6, caused by downstreamobstruction. The base 25 of the container 6 is lined with a layer,typically 75 mm thick, of smooth formed concrete 28. A polythenemembrane 29, typically 1200 g on 50 mm sand blinding, ensures againstwater escaping from the container 6 to attack the foundations 24. Italso diminishes the possibility of the occurance of ground heave in claysubsoils.

In FIG. 5, a section of the garage floor 23 can be seen showing theposition of the air bricks 16 in the side walls 17,18 of the garage. Thefloor typically comprises 100 mm thick blocks 31 and P.C. concrete beams32, lined with an A96 mesh 33 and covered with a 50 mm structuraltopping 34. Each air brick 16 is fitted with an insect screen 35 toprevent debris entering the container 6.

In use, stormwater is collected and drained from the property by thedrainage means 5 provided on the property 2,2 a. The stormwater passesthrough outlet pipes 4 and enters the control chamber 3 at the doublegarage 2 a.

Stormwater continues to enter the control chamber 3 until the waterlevel W is reached. Once the water level rises above the water level W(as shown in FIG. 3), stormwater begins to drain into the adjacentsubterranean container 6 located underneath the garage 2 a.

As the stormwater drains into the container 6, it also enters viaorifice 21 the outlet pipe 7 and is directed to the nearby sewer 8,joining stormwater draining from neighbouring properties (not shown) onthe way.

In the event of serious flooding, when the water level in the container6 rises above the level M (as shown in FIG. 3), stormwater can thenleave also by way of the open end 13 of the pipe 7, which functions as astormwater overflow in the control chamber 3. Furthermore, if thecontainer 6 is filled to capacity with stormwater through obstruction,the excess stormwater can escape through the air bricks 16 located inthe side walls 17,18 of the double garage 2 a.

An alternative embodiment of the control chamber is shown in FIGS. 6 and7. This chamber 3 is formed solely from plastics material, preferablyUPVC. As such it is easily located adjacent to the container 6 shown inFIG. 2. It may be attached to a wide variety of other storagecontainers.

The control chamber 3 is functionally very similar to the hand-builtembodiment of FIG. 3. It is of broadly cylindrical form, with apreferred diameter of approximately 475 mm. Two inlet pipes 4,preferably of approximately 100 mm diameter each, lead into an outersection 36 of the control chamber 3, which is separated by a weir 37from an inner section 38 of the control chamber 3. The weir 37 providesa trap for silt and debris, preventing this from entering the innersection 38 of the control chamber.

An outlet pipe 39 replaces the holes 14 as the inlet to the container 6.It leads from the inner section 38 of the control chamber 3 to thecontainer. The pipe 39 is preferably of approximately 150 mm diameter.As water in the control chamber rises stormwater enters the outletconduit from the outer section 36 of the control chamber through theorifice 21 in the bottom of the outlet conduit.

The water accumulates in the outer section 36 of the control chamber 3.As the water level in this section rises silt and debris settles to thebottom of the outer section 36 and only water decants over the weir 37to the inner section 38 of the control chamber.

The outlet 39 allows stormwater to enter the container 6 when the waterrises above the water level W. In the event of serious flooding, whenthe water level in the container rises above the level M, stormwater canthen leave also by way of the open end of the pipe 7, which functions asa stormwater overflow in the control chamber 3.

Studies have shown that when collection of stormwater in the controlchamber 3 and container 6 abates, the water level therein typicallytends to fall by approximately 50 mm each half hour. Therefore, in theoccurrence of a thirty year storm event, the storage, comprising thecontainer 6 and the control chamber 3, would empty in one and a halfhours and in the occurrence of a one hundred and fifty year storm event,the storage would empty in two and a quarter hours.

The controlled discharge from the control chamber and container is, in apreferred example of the embodiment described, limited by the orifice 21to 1 litre per second. As a result, the flow through the sewer system 8will be greatly reduced, thereby enabling installation of smallercapacity off-site storm sewers and the possible elimination ofbalancing, or reduction of size of balancing. By distributing thestorage throughout the development within a private drainage system, themaintenance responsibilities of the Water Authority will also be greatlyreduced.

The risk of downstream flooding is significantly reduced. If conduitsdraining a large balancing pond or tank of the prior art type becomeblocked, localised flooding could occur. Flood risks are significantlyreduced by distributing several storage areas, as shown in the example,around the property development 1.

In the event of, for example, a 300 mm diameter sewer being used insteadof a 600 mm diameter sewer at a property development, by use of theapparatus according to the first aspect of the invention, the developerwill save in costs of materials, there will be a reduction in dig (toinstall the sewer) and the adjacent foul sewer will be made shallower inthe case of a dual trench sewer construction. Furthermore, considerablesavings will be made by the possible elimination of a balancing meanssuch as a large tank or pond on land which could otherwise be used fordevelopment.

Once the water level in the container 6 has fallen, there will be areservoir of stormwater in the container which cannot escape through theholes 14 into the control chamber 3 as the water level is notsufficiently high. This creates a permanently wetted area beneath thegarage, typically approximately 3m³ per dwelling. Typically, in thedouble garage 2 a, this means deepening the garage tanking byapproximately 120 mm per dwelling.

The permanently wetted area may be used to provide water, for example,for washing a car, flushing a toilet or watering the garden if asuitable pump is fitted.

What is claimed is:
 1. A stormwater retention apparatus to retainstormwater prior to release of the stormwater from a property,comprising: a closed container located underneath or proximal to abuilding of the property, being operatively connected by at least oneinlet conduit to drainage means sourced externally from the building toreceive stormwater into the container, and being further operativelyconnected to at least one outlet conduit by which stormwater is led awayfrom the container; and a control chamber with which the container is influid communication and through which stormwater enters and is to bestored in, and leaves the container when the stormwater reaches adetermining level in the control chamber spaced above the base of thecontainer, wherein the inlet and outlet conduits are connected to thecontrol chamber and thereby to the container, and that the outletconduit comprises an end portion which passes out of the control chamberand includes an entry spaced above the determining level by whichstormwater can pass from the control chamber into the end portion toexit from the control chamber, and which by being spaced above thedetermining level thereby allows stormwater to collect in the containerand control chamber above the determining level.
 2. The stormwaterretention apparatus according to claim 1 characterized in that the inletconduit is disposed above the level of the entry of the end portion ofthe outlet conduit.
 3. The stormwater retention apparatus according toclaim 1 characterized in that the outlet conduit is in fluidcommunication with a local drainage network on exit from the container.4. The stormwater retention apparatus according to claim 1 characterizedin that the outlet conduit is in fluid communication with a system forreusing stormwater.
 5. The stormwater retention apparatus according toclaim 1 characterized in that the container is less than 7 m³ in volume.6. The stormwater retention apparatus according to claim 1 characterizedin that the container is made at least in part of bricks and mortar andis lined with a damp proof membrane and concrete.
 7. The stormwaterretention apparatus according to claim 1 characterized in that the inletand outlets conduits are pipes.
 8. The stormwater retention apparatusaccording to claim 7 characterized in that the pipes have a diameter ofabout 75 mm to 150 mm.
 9. The stormwater retention apparatus accordingto claim 1 characterized in that exit rate limiting means is providedwhereby the rate of discharge from the apparatus is limited.
 10. Thestormwater retention apparatus according to claim 1 characterized inthat the end portion of the outlet conduit has an orifice in the controlchamber at the determining level whereby a restricted flow of stormwateris allowed to pass through the orifice into the outlet conduit whenstormwater reaches the determining level in the control chamber andbefore the level of stormwater in the control chamber reaches the entryof the end portion.
 11. The stormwater retention apparatus according toclaim 10 characterized in that the end portion has a substantially 90°bend whereby one open end of the end portion is directed upwardly awayfrom the base of the control chamber and forms the entry, and theorifice is provided in the end portion at an underside of the bend. 12.The stormwater retention apparatus according to claim 1 characterized inthat the control chamber is located for use below ground level.
 13. Thestormwater retention apparatus according to claim 1 characterized inthat the control chamber and the container are so related in use thatthe stormwater passes under gravity from the control chamber into thecontainer.
 14. The stormwater retention apparatus according to claim 1characterized in that the control chamber further comprises a trap fordebris.
 15. The stormwater retention apparatus according to claim 14characterized in that the trap comprises a weir disposed between a partof the control chamber at which stormwater is received from the inletconduit and a part of the control chamber in fluid communication withthe container.
 16. The stormwater retention apparatus according to claim1 characterized in that the outlet conduit further comprises means atthe entry to prevent debris entering the outlet conduit from the controlchambre and prevents access for pests into the control chamber from theoutlet conduit.
 17. The stormwater retention apparatus according toclaim 16 characterized in that the means to prevent debris enteringcomprises a bird-cage cap fitted to the entry.
 18. The stormwaterretention apparatus according to claim 1 characterized in that itfurther comprises a pump means for expelling stormwater from thecontainer.
 19. A system comprising a building having a stormwaterretention apparatus according to claim 1, wherein the container islocated underneath or proximal to the building.
 20. The system accordingto claim 19 comprising a series of buildings each of which hasstormwater retention apparatus according to any of claims 1 to 18, thestormwater being retained at each apparatus exiting from the containerthereof by way of the respective control chamber into a communal localsewer or water course.
 21. The system according to claim 19characterized in that the container of the stormwater retentionapparatus is located underground.
 22. The system according to claim 19characterized in that the building comprises a house having a garage,the container of the stormwater retention apparatus being disposedunderneath the garage.
 23. The system according to claim 19characterized in that the container is incorporated into the foundationof the building.
 24. The system according to claim 19 characterized inthat the drainage means to which the stormwater retention apparatus isconnected comprises guttering and drainpipes which channel thestormwater to the base of the or the respective building and into thecontainer of the apparatus.
 25. The system according to claim 19characterized in that air bricks are provided in the portions of thebuilding proximal to the respective container.
 26. The system accordingto claim 19 characterized in that condensation isolation means isprovided adjacent the container of the stormwater retention apparatus toprotect the respective building from the effect of dampness.
 27. Thesystem according to claim 26 characterized in that the condensationisolation means comprise polythene membranes and a waterproof coating.28. A method of retaining and controlling discharge of stormwatercollected by drainage means fitted to a building, the method comprisingthe steps of: collecting stormwater by drainage means; retaining thestormwater by a stormwater retention apparatus comprised of a closedcontainer which is located underneath or proximal to a building of theproperty, being connected by at least one inlet conduit to drainagemeans sourced externally from the building to receive stormwater intothe container, and being further connected to at least one outletconduit by which stormwater is led away from the container and a controlchamber with which the container is in fluid communication and throughwhich stormwater enters and is to be stored in, and leaves the containerwhen the stormwater reaches a determining level in the control chamberspaced above the base of the container, wherein the inlet and outletconduits are connected to the control chamber and thereby to thecontainer, and that the outlet conduit comprises an end portion whichpasses out of the control chamber and includes an entry spaced above thedetermining level by which stormwater can pass from the control chamberinto the end portion to exit from the control chamber, and which bybeing spaced above the determining level allows stormwater to collect inthe container and control chamber above the determining level; andcontrolling release of the retained stormwater by the stormwaterretention apparatus into local drainage facilities.
 29. The method ofretaining and controlling discharge of stormwater according to claim 28characterized in that the stormwater retention apparatus has thecontainer for retention of the stormwater disposed underneath a garageof the building.